Is your face linked in to my space?

Okay, I need a little help. Facebook.  MySpace.  LinkedIn.  Squidoo.  Etc. etc.

Is it just a bunch of busy work to maintain them all?  Or, am I going to be sorry if I miss out on one now?

Paul Jacobson over at BizTips asks if Facebook is the new LinkedIn.  Does that make LinkedIn the old MySpace?

How are they different?  Do I really need them all?  Do I need any of them? How should I use them? How do you use them?